The present invention relates to a fluid machine such as a pump or the like, and more particularly to a fluid machine which detects the temperature of a fluid being handled, prevents shut-off operation of a pump or the like, or changes the flow rate or pressure of the fluid based on the detected temperature of the fluid being handled.
Generally, when the shut-off operation of a pump is carried out for a long period of time, the pump causes trouble. Specifically, since the liquid being handled by the pump is expanded by a rise in the temperature of the liquid in the pump, the pressure in the pump increases, resulting in damage to the pump casing.
It is also known that when the handled liquid is evaporated and atomized, the service life of a mechanical seal and a gland packing is reduced. If the pump is of such a structure that the handled liquid is used to lubricate bearings and cool the motor, then the evaporated and atomized liquid also reduces the service life of the bearings and the motor. Heretofore, if the shut-off operation of a pump is unavoidable due to system requirements, then it has been customary to protect the pump with a relief pipe or the like in the shut-off operation.
However, when the relief pipe is used, it may accidentally bring about shut-off operation due to a rust based clog in the relief pipe or erroneous operation of the valve of the relief pipe.
Facilities for producing cooling water with a cooling tower and a circulating pump are continuously operated irrespective of the temperature of the liquid, and often consume more electric power than necessary.
There is also a system in which some units, i.e., a fan and a pump of a cooling tower, are operated when the temperature of the liquid rises, and they are shut down when the temperature of the liquid falls. Though this system is a better energy saver than the former facilities, it may fail to supply desired cooling water because the temperature of the liquid varies depending on the temperature settings for turning on and off the thermostat. If the range in which the temperature of the liquid is variable is reduced, then the above units need to be started and shut down more frequently, and hence suffer maintenance problems.
In view of the above conventional problems, it is a first object of the present invention to provide a method of preventing the shut-off operation of a pump for protecting the pump from the shut-off operation, and a pump unit which employs such method.
A second object of the present invention is to provide a fluid machine which. recognizes the temperature of a fluid by itself and employs the recognized temperature in coordination with the flow rate or pressure of the fluid to allow the entire system to save more energy.
To achieve the first object described above, in a method of preventing shut-off operation of a pump according to a first aspect of the present invention, the temperature of a handled liquid in the pump is detected, and the pump is shut down if an increase in the temperature per time of the handled liquid is greater than a predetermined value.
According to the first aspect of the present invention, the pump is reliably protected from shut-off operation. When the pump is operated normally, it should not be operated in error. In applications for circulating hot water, the temperature of the handled liquid passing through the pump may abruptly change as in the following case. For example, at the same time that the pump is actuated, hot water is supplied from a heat source on a suction side.
For preventing the pump from being operated in error, in a method of preventing shut-off operation of a pump according to a second aspect of the present invention, a temperature of a handled liquid in the pump is measured in a predetermined time (xcex94T) at a plurality of (N) times, and the pump is shut down if an increase in the temperature across the predetermined time is greater than a predetermined value (xcex94t) at (Nxe2x88x921) times.
The method according to the second aspect of the present invention is capable of preventing the pump from being operated in error.
specifically, the temperature of the handled liquid is measured N times, e.g., six times, each in the predetermined time (xcex94T), e.g., 1 minute. If all the temperature differences between first and second measurements, second and third measurements, third and fourth measurements, fourth and fifth measurements, and fifth and six measurements are 2xc2x0 C. or higher, then the pump is shut down. In this manner, even if the temperature of the handled- liquid is changed (increased) transiently in normal operation of the pump, the pump is prevented from being shut down in error.
In order to recognize the gradient of the increase in the temperature of the handled liquid in the pump, it is necessary to measure the temperature at least across, i.e., before and after, the predetermined time. Therefore, it is time-consuming to recognize the gradient of the increase in the temperature of the handled liquid. However, if a shut-off operation of the pump occurs while the pump is operating at the upper limit of the temperature range according to pump specifications, then the pump needs to be shut down as soon as possible because the temperature of the liquid in the pump exceeds the specification range in a short period of time.
In a method of preventing shut-off operation of a pump according to a third aspect of the present invention, the pump is shut down if a temperature of the handled liquid in the pump, other than the increase in the temperature per time of the handled liquid, becomes equal to or higher than a predetermined value (T). In this manner, the pump is protected from suffering the above problems.
A pump unit according to an aspect of the present invention has a pump, a motor for actuating the pump, a temperature detecting device for detecting the temperature of a handled liquid in the pump, and a control circuit electrically connected to the temperature detecting device for controlling operation of the motor; wherein the pump is shut down if an increase in the temperature, detected by the temperature detecting device, per time of the handled liquid is greater than a predetermined value.
In this invention, the pump unit has a frequency converter assembly for supplying electric power to the motor, the control circuit being disposed in the frequency converter assembly.
Recently, there have been used pump units having a pump, a motor, and a frequency converter (inverter) that are integrally combined with each other. These pump units are products that are primarily designed as an energy saver. In such a pump unit, a temperature detecting device is disposed in a pump casing, and connected to the control circuit in the frequency converter assembly for protecting the pump from shut-off operation.
Since the frequency converter has a circuit for storing and processing supplied information to control an output signal to the motor, it is easy to protect the pump by recognizing the gradient of the increase in the temperature of the handled liquid, as described above.
According to another aspect of the present invention, a pump unit for shutting down a pump after a shut-off operation of the pump when the amount of liquid supplied from the pump is reduced, characterized in that the temperature of a handled liquid in the pump is detected, and the pump is shut down if an increase in the temperature per time of the handled liquid is greater than a predetermined value.
In order to achieve the above second object, a fluid machine for delivering a fluid according to an aspect of the present invention, characterized in that a flow rate or pressure of the fluid is changed depending on the temperature of the fluid or the change in the temperature of the fluid based on a predetermined control program.
In the fluid machine according to the present invention, since the temperature of the handled fluid is recognized, and the flow rate or pressure of the fluid can be changed depending on the temperature of the fluid or the change in the temperature of the fluid, the energy consumed by the overall system can be saved. In a preferred aspect, the flow rate or pressure of the fluid is changed in order to keep the temperature of the fluid substantially constant. The flow rate or pressure of the fluid is changed by adjusting the rotational speed of the fluid machine which is a turbo-type fluid machine.
In the fluid machine according to the present invention, a target reference temperature for the fluid is predetermined, and the actual temperature of the handled fluid is detected by the temperature detecting device. If there is a difference between the reference temperature and the actual temperature of the fluid, then the rotational speed of the fluid machine is increased or decreased to reduce the difference between the reference temperature and the actual temperature of the fluid.
According to a preferred aspect of the present invention, a fluid machine is characterized by a pump unit comprising a pump, a motor for actuating the pump, and a frequency converter assembly for controlling the motor to change its speed, and further characterized by a temperature detecting device disposed in the pump unit, the arrangement being such that a signal from the temperature detecting device is supplied to a controller in the frequency converter assembly. A switch is disposed in the frequency converter assembly for changing the reference temperature stepwise.
According to an aspect of the present invention, a temperature detecting device for detecting the temperature of air is separately disposed around the fluid machine, and the preset reference temperature is automatically changed based on a detected signal from the temperature detecting device. In this structure, the fluid machine can be operated in view of the temperature of the ambient air for allowing the overall system to save more energy.